Pyribencarb or methyl={2-chloro-5-[(E)-1-(6-methyl-2-pyridylmethoxyimino)ethyl]benzyl}carbamate, which is an agrochemically active component, is a known benzyl carbamate-based bactericide, which is disclosed in Patent Document 1 for the first time. Non Patent Document 1 discloses that it is characterized by having a wide range of control spectrum and exerts an excellent controlling effect on diseases of fruits and vegetables such as gray mold, crown rot, brown rot and the like, caused by various phytopathogenic fungi including ascomycetes.
Dusts, granules, wettable powders, water-dispersible granules, solutions, aqueous suspensions, emulsifiable concentrates and the like are known as forms of agrochemical preparations that have hitherto been put into practical use. Among such agrochemical preparations, an aqueous suspension, i.e., a liquid agrochemical preparation herein particulates of an agrochemically active component relatively insoluble in water are suspended in water, is a widely used form of preparation from the following reasons: there is no dusting at the time of use and there is less concern that a user is exposed to agrochemical preparations; it is easy to weigh; and it is highly safe because it does not use an organic solvent which has adverse effects on the human body and the environment and has low flash point, etc.
In certain aspects of applying the aqueous suspension to agricultural land or non-agricultural land, the aqueous suspension may be applied as it is as a spray solution. However, the method wherein the aqueous suspension may be diluted in a predetermined amount of water to ensure a sufficient liquid volume, and the resulting diluted solution may be applied as a spray solution is generally employed.
Here, the typical methods for applying the spray solution are roughly divided into: ground spraying using a knapsack-type powered sprayer, a boom sprayer, a speed sprayer or the like; and aerial spraying from the air using an aircraft such as a fixed wing machine or a rotary wing machine, equipped with a sprayer. The latter aerial spraying is advantageous in that it can carry out agrochemical treatment in a labor-saving manner on a wide area of agricultural land, etc. However, the amount of spray solution that can be loaded on an aircraft may be inevitably restricted by the load capacity of the aircraft determined by its power performance or the like. Particularly, an unmanned helicopter or a compact unmanned rotary wing machine for spraying agrochemicals, which is commonly referred to as RC (radio control) helicopter, usually has a spray solution amount that can be loaded of about 10 to 24 kg, and thus the amount of the spray solution that can be applied at one flight is limited.
In the case of ground spraying, the aqueous suspension may be added to the predetermined amount of water to prepare a spray solution usually in an amount about 500 to 4,000 times the amount of the aqueous suspension. If it is attempted to apply a large amount of spray solution prepared in this way using the RC helicopter mentioned, above, it is necessary to repeat frequent takeoff and landing and replenishment of spray solution, which is troublesome and non-labor saving. Therefore, for aerial spraying, it is routinely practiced to apply a spray solution usually at about 4 to 32 times of dilution factor, which means much higher concentration than that for ground spraying.
However, with a spray solution of an aqueous suspension prepared at a high concentration with a low dilution factor, a problem which is rarely discussed for a dilute spray solution for ground spraying has become apparent. That is, since the concentration of the agrochemically active component particulates in the diluted solution becomes high, the amount of the agrochemically active component particulates that precipitate considerably increases in proportion to the concentration. Moreover, the deposited layer of the precipitated agrochemically active component particulates form a hard cake in a tank in which the aqueous suspension agrochemical composition is formed or a chemical tank of an aircraft, resulting in a problem of poor dispersion. Since the agrochemically active components which have been converted into a hard cake cannot be discharged from the spray nozzle, not only the desired agrochemical treatment cannot be performed, but also the piping in the spraying machine may be clogged, resulting in a failure. The problem varies in severity depending on the chemical species of the agrochemically active component, and some deposited layers may not become a hard cake. Anyway, pyribencarb has a strong tendency to form a hard cake. Therefore, in order to establish an aqueous suspension of pyribencarb for aerial spraying, technology to formulate preparation while preventing hard cake formation in a spray solution at low dilution factor is required.
As a prior art example of suppressing hard cake formation in a diluted solution of an agrochemical composition, Patent Document 2 discloses a method for preventing solidification of precipitate in a diluted solution of the agrochemical preparation, characterized in that an agrochemical preparation is diluted with water, then a coagulation inhibitor such as aluminum sulfate, polyaluminum chloride, ferric sulfate, carboxymethyl cellulose, poly-acrylic acid ester, polyvinyl alcohol, alginic acid salt, polyvinyl pyrrolidone chitosan is added in, such an amount that generation of aggregates is not observed for at least 15 minutes after addition of the coagulation inhibitor. However, polyacrylic acid salt has not been mentioned. The document also describes that, in the case of a liquid preparation such as a suspension preparation, previously blending above-mentioned coagulation inhibitor in an agrochemical preparation promotes aggregation of the agrochemically active component in the preparation, and results in remarkably inferior inhibition effect on solidification of precipitate compared to the case wherein the coagulation inhibitor is added at the time of dilution. The function of preventing formation of a hard cake at the time of preparing the spray solution of an agrochemical composition at low dilution factor has not been imparted by itself to the agrochemical composition.
Patent Document 3 discloses an aqueous suspension agrochemical preparation characterized in that particulates of a hydrophobic solid agrochemically active component are dispersed in a water by means of a water insoluble solvent which is a good solvent of the agrochemically active component and a surfactant Patent Document 3 also describes that carboxymethyl cellulose, polyvinyl alcohol, polyacrylic acid or a salt thereof, alginic acid salt, polyvinyl pyrrolidone, gum arabic, xanthan gum, gelatin, white carbon, talc, bentonite, clay or the like may be used as a thickener for preventing aggregation or precipitation in the preparation, if desired. The document provides a technique to improve the aggregation/precipitation of solid particles caused by long-term preservation of the aqueous suspension agrochemical preparation of the agrochemically active component having a low melting point. However, the technology includes a water insoluble organic solvent as an essential constitutional requirement and sacrifices the inherent safety which is indicated as an advantage of the aqueous suspension. Moreover, the aqueous suspension agrochemical composition of the invention in the document cannot be expected to suppress formation of hard cake in a spray solution diluted at high concentration with low dilution factor at the time of use. There were no findings on an aqueous suspension agrochemical composition of pyribencarb with performance suitable for aerial spraying.